This invention relates generally to a process and system for the oxidation of engine emission prticulates deposited in a particulate filter trap, by supplying secondary energy.
Systems have been developed for the treatment of diesel engine exhaust gas to reduce particle emission to render the exhaust gas as free of harmful substances as possible. Such systems primarily employ trap filters which trap and collect the particulates as the exhaust gas flows therethrough. However, the particulates deposited in the filter may produce increased flow resistance in the exhaust system which thereby increases the engine's back pressure. And, an increased concentration of particulates may, as a function of load and rpm, cause the engine to stall. It therefore becomes necessary to remove the particulates deposited in the filter continuously or intermittently, which is generally carried out by oxidation of the deposit of particulates.
Reliable filter systems for trapping the particulates with continuous or intermittent particulate combustion are, for example, in the form ceramic filters with a honeycomb structure, steel wool filters and ceramic foam filters with or without catalytic coating.
Various approaches have been taken in regenerating the particulate filters in which the collected particulates are intermittently burned to thereby lower the particulate emission of diesel engines. For example, in order to achieve regeneration of particulate filters, it was necessary to increase the exhaust gas temperature to such an extent that the deposited particulates were ignited and oxidized. However, this combustion required a great deal of energy.
A self-contained particulate oxidation is based on the knowledge that heat released during exothermic reactions is at equilibrium with the heat removed by the exhaust gas. If the removal of heat exceeds the released exothermic heat, the rate of oxidation falls below the rate at which particulates are deposited in the filter. This causes the particulate mass in the filter to rise. If, on the other hand, the rate of oxidation is larger than the heat removed, more particles are oxidized than the engine can move into the filter which thereby causes the particulate mass to decrease.
Steps have been taken in known systems to reduce heat removal by the expedient of increasing the exhaust gas temperature by operation of the engine or from a secondary energy source to such an extent that the reaction rate is significantly increased and the heat removal drops because of higher exhaust gas temperature.
To achieve the filter regeneration which is independent and is energy efficient and utilizes the exothermic energy of particulate oxidation, it is possible to reduce heat removal or to attempt to increase the reaction rate.
An S.A.E. Paper 1985/850014, entitled "Advanced Techniques for Thermal and Catalytic Diesel Particulate Trap Regeneration", discloses a technique for regenerating diesel particulate traps employing secondary heat energy by the provision of an electric resistance heater, and an additional air supply.